Early kinetics of large molecule transport between plasma and lymph in dogs

Using a mathematical model in which the interstitial space resembled a gel filtration column, Watson and Grodins (Microvasc. Res. 16: 19-41, 1978) predicted that molecules larger than serum albumin should have an early approach to steady state in lymph faster than that of serum albumin. This hypothesis was tested in dogs anesthetized with pentobarbital sodium by use of radiolabeled albumin and fibrinogen and a fluorescent dextran and by collecting lymph from cannulas in the prepopliteal lymphatics of the hind paws. The steady-state lymph-plasma concentration ratios (R), measured chemically, were 0.24 +/- 0.02 (SE, n = 16) for albumin and 0.040 +/- 0.004 (n = 16) for fibrinogen. In 5 h, albumin and fibrinogen tracers had reached approximatly 25 and 50% of their steady-state levels, respectively. The dextran (mol wt 1.5 x 10(5)) behaved like fibrinogen. The data support the hypothesis that the interstitium has nonrestricting pathways, and that there are gel regions that have a low permeability to very large molecules.